When sending emails, though, you need to strike a balance that lets you maximize the advantages without annoying your customers. It's a fine line to walk. Without the right approach, you run the risk of spamming your email list. That's a great way to make your customers mad and lose followers.

Before you shrug your shoulders and decide that you'll send emails whenever you think it's appropriate, consider that more than 269 billion emails get sent every day. When you look at the average, that means that the 3.7 billion email users around the world receive 72 emails per day.

If customers feel like you're contributing to their glut of emails, then many of them will see you as a spammer and decide to opt out of your email list.

No one wants to look at that many messages in one day. If customers feel like you're contributing to their glut of emails, then many of them will see you as a spammer and decide to opt out of your email list. Perhaps even worse, they may mark your emails as spam, which means you'll waste resources sending emails that get caught in spam folders instead of reaching customers.

You don't want that, so take some time to think carefully about whether you're spamming your email list and how many emails you can send customers before you become a nuisance.

Know what recent research says about email preferences

In 2015, a survey found that about 88 percent of people like to receive promotional emails "at least once per month." Slightly more than 60 percent said that they like receive promotional emails "at least weekly." About 31 percent liked getting weekly emails.

88 percent of people like to receive promotional emails "at least once per month."

The survey results fall dramatically when people receive promotional emails more than once per week. About 15 percent said that they like getting daily emails. 10 percent responded that they prefer receiving promotional emails twice a week. Only 3 percent said that they like getting the emails three times a week.

Results from this survey show that most people prefer getting promotional emails at least once a week or once per month.

Measure your click-through rate (CTR) to see how recipients respond to emails

Trends, of course, can change significantly over a few years. Trends can also vary depending on industry and demographics. You don't have to rely on surveys to determine whether customers find your emails useful, though. Instead, you can measure your clickthrough rate to determine how many recipients engage with your emails.

The ecommerce industry has an average email opening rate of 15.66 percent and a CTR of 2.07 percent

According to MailChimp, the ecommerce industry has an average email opening rate of 15.66 percent and a CTR of 2.07 percent. If your ecommerce store doesn't get similar results, then you're not keeping up with the industry average. A lower open rate or CTR could suggest that you're not sending the right number of emails.

There are, however, other reasons that customers may not open your emails or follow links. Before you adjust the number of emails that you send, make sure that your marketing campaigns:

Use engaging subject lines.

Include information and offers that your customers find useful.

Mix text with images to create a pleasant experience.

Never mislead customers.

Personalize your messages.

As long as you have a carefully crafted campaign, you can consider your CTR a comment on whether customers want to receive emails from your store. If they aren't even opening your emails, then you're probably frustrating them with too many messages.

Adapt your email frequency to what customers prefer

You don't have to rely on questionable statistics to determine how many emails you should send your customers. Instead, you can ask them how many promotional messages they prefer to get from you.

Create a short survey that includes a question about how many emails your customers prefer. You can give them the survey when they:

Join your email list.

Make a purchase.

Open a recent email.

Keep in mind that today's email marketing software gives you a lot of flexibility. You don't have to choose a specific number of emails to send. Depending on your survey results, you may decide to engage with some customers by sending weekly emails while other customers only receive monthly emails.

Divide your customers into categories so you can customize their experiences.

Make sure your emails serve a purpose

Sending frequent emails doesn't necessarily mean that you're spamming your customers. The content of your emails will affect the way that people perceive them. You may find that you can send daily emails to some subscribers as long as you give them useful, entertaining content. The same people may decide that your emails are spam, though, if you don't give them content that they want to read.

Make sure that all of your emails serve a purpose. No one wants an inbox full of drivel, but most people want to get messages that they enjoy reading. What your emails contain, therefore, could determine whether people open the messages or mark them as spam.

Finding the right number of emails to send your customers requires insight and planning. There isn't a magic number that works for everyone. Pay close attention to how people respond to your emails and ask them to give you feedback. It won't take long before you find a balance that most people find useful.